MicroRNA loci support conspecificity of Gyrodactylus salaris and Gyrodactylus thymalli (Platyhelminthes: Monogenea)

The monogenean flatworm Gyrodactylus safaris is a serious threat to wild and farmed Atlantic salmon stocks in Norway. Morphologically, the closely related but harmless Gyrodactylus thymalli on grayling can hardly be distinguished from G. safaris. Until now, molecular approaches could not resolve unambiguously whether G. safaris and G. thymalli represent just one polytypic species, two polytypic species or a complex of more than two species. In the first known genome-wide analysis utilizing 37 conserved microRNA loci, the genetic differentiation of seven populations of G. safaris and G. thymalli was assessed. The concatenated alignment spanned 21,742 bp including 62 variable positions. A neighbor-joining cluster analysis did not support any host-based or mitochondrial haplotype-based grouping of strains. We conclude that a two species concept for G. safaris and G. thymalli does not reflect meaningful biological entities. Instead, G. safaris and G. thymalli are just one species comprising several pathogenic and non-pathogenic strains on various primary hosts. Following the International Code for Zoological Nomenclature, G. safaris Malmberg, 1957 is the valid species name with G. thymalli Zitnan, 1960 becoming the junior synonym. Accordingly, the range of G. safaris is significantly increased, given that formerly G. salaris-free countries such as e.g., Great Britain are now within the species' natural range. The synonymization of G. safaris and G. thymalli implies severe challenges to current disease management routines, which assume that G. safaris and G. thymalli are readily distinguishable. Protocols for reliable identification of pathogenic and non-pathogenic strains of G. safaris need to be developed. (C) 2014 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.